Rendering appears all grainy and dark after using Diffuse BSDF
Your matierial is flawless and gorgeous. It's your lighting setup you need to fix. Move your lamp a little further away from your objects and crank up the strength. I put it about halfway between your objects and your camera and put the strength to 3000. Also on the lamp, lower the bounces. If dark sharp shadows are what you're going for, lower the size of the lamp to zero, as well. That will reduce some of the graininess. A lot of it is also simply render samples. Go to your light paths and pick 'Global Illumination' from the dropdown. Increase your render passes to 200 or higher. If you find it's rendering slowly, go to performance and change the tile size to a multiple of 8. (I just went with 8).